A typical prior art structure for mounting disks of a disk drive to the spindle of a drive motor is shown in FIG. 1. As shown therein, a disk drive motor 20 includes a spindle 22 which is rotatable about an axis of rotation 24. A first disk 26 includes a central aperture 28 through which the spindle 22 is disposed, one side 30 of the disk 26 at its inner periphery being in contact with an annular spindle surface 32 which is perpendicular to the rotational axis 24 of the spindle 22. An annular spacer 34 is fitted about the spindle 22, and has a surface 36 perpendicular to the axis of rotation 24 and in engagement with the inner periphery of the disk 26 on the opposite side 38 of the disk 26. Another disk 40 has a central aperture 42 through which the spindle 22 is disposed, the disk 40 at its inner periphery having one side 44 in engagement with surface 46 of the annular spacer 34, which surface 46 is perpendicular to the axis of rotation 24 of the spindle 22. A single-piece stamped or formed disk spring clamp 48 is fixed to the spindle 22 by means of screw 50 and has an annular portion of U-shaped cross section adjacent its outer edge 52 for engagement with the inner periphery of the disk 40 on the opposite side 54, to force the disk 40 in a direction downward as shown in FIG. 1.
It will be understood that one of the key parameters for optimum performance of disk drives is the flatness of the installed disks. In general, the best flatness is achieved when the disk is mated against very smooth, flat surfaces on both sides of the disk.
Because of the configuration of the conventional disk spring clamp 48, when clamping force is applied to the surface 54 at the inner periphery of the disk 40, a small radial force is applied to the disk 40 (away from the axis of rotation 24) in addition to the forces parallel to the rotational axis 24.
Several problems exist with the conventional disk spring clamp 48 of FIG. 1. For example, surface finish and flatness is very difficult to achieve and maintain at the region where the disk spring clamp 48 contacts the disk 40. The forming or bending process of the disk spring clamp 48 often creates microcracks in the clamp 48 at the portion of U-shaped cross section that touches the disk 40. Furthermore, the clamping force applied to the disk 40 is not uniform. This is due to the anisotropic nature of rolled sheet stock used to form the clamp 48, the forming process itself, and the screw head torque warping the clamp 48 during installation. All of these forces are transmitted through to the disk 40.
Furthermore, installation and application of the clamp 48 creates contamination and residual stresses. As the axial force is applied via the screw, the point at which the clamp contacts the disk translates and rotates due to the deflection being induced in the clamp 48. This relative motion galls the soft aluminum disk surface resulting in particulate formation. The resultant and residual radial force contributes to an out-of-flat disk.